1. Field of the Invention
This invention relates to a surface-type optical apparatus, such as a light source apparatus for emitting evanescent light or the like, suitable for use in a so-called near-field optical microscope, and an information recording or optical exposure apparatus using a near-field optical system, its fabrication method, and its use method of use as an optical information recording apparatus, an optical exposure apparatus or the like.
2. Related Background Art
Recently, the development of optical techniques using evanescent light from a minute opening of less than about 100 nm formed at a sharp probe tip has been energetically advanced. Such optical techniques include high resolving-power observation, high-density information recording, super-fine optical exposure and the like utilizing the near-field optical system. Regarding the high resolving-power observation, During et al., J. Appl. Phys., vol. 59, 3318 (1986) discloses a scanning near-field optical microscope (SNOM) for investigating a sample surface by detecting the condition of the sample surface with an optical probe. Further, Japanese Patent Application Laid-Open No. 5 (1993)-100168 discloses an apparatus for introducing light into the SNOM. In this apparatus, as illustrated in FIGS. 1 and 2, a minute opening 610 is formed at a tip of a conical member mounted on an Si substrate 601, an aperture portion 602 is formed in the Si substrate 601, and an optical fiber 603 is inserted into the aperture portion 602 to emit light through the fiber 603. There are also provided an electrode 607, a light waveguide layer 608, a metal layer 609 and an antireflection layer 611.
Further, there has been proposed a structure, as illustrated in FIG. 3, wherein a minute opening 813 is formed in an electrode 811 on the light emitting end surface of a surface emitting laser. The surface emitting laser includes a laser substrate 801, a buffer layer 802, a semiconductor multi-layer mirror 803, current-constricting semiconductor layers 804, 808 and 809, an active layer 805, a cladding layer 806, a contact layer 807, an insulating layer 810, and another laser electrode 812. In this structure, another optical system needs to be arranged for a photodetector for observing a sample image or reading optical information.
Furthermore, Japanese Patent Application Laid-Open No. 8 (1996)-306062 discloses a structure, as illustrated in FIG. 4, wherein an elliptically-conical probe 903 is provided on one end facet of an end-facet emitting semiconductor laser 901. The probe 903 is covered with a Pt electrode 910, and a member with a minute opening for generating evanescent light 904 is formed at a tip of the electrode 910. This structure further includes a photodetector 902, and a floating slider 906, and an optically-recorded region 909 is formed in an optical recording medium. In this structure, the photodetector 902 is mounted on the other end facet of the laser 901 to detect its light output. Thus, the light introducing apparatus and the signal reading apparatus are provided in one optical system, and a compact optical head for reading optical information is achieved.
In the near-field optical system, a high efficiency of the light source is required, since evanescent light leaks slightly from the minute opening. Therefore, a semiconductor laser with a low threshold and a high quantum efficiency is needed. The structure illustrated in FIGS. 1 and 2, however, is undesirable, because light is guided through the optical fiber 603 and hence coupling loss is likely to occur. Further, the SNOM head with the end-facet emitting laser 901, as illustrated in FIG. 4, is unsuitable for multiple arraying since its operational current and consumption electric power are large.
Furthermore, in the near-field optical system, its probe needs to be supported by a certain elastic or resilient body because the probe must be scanned in such a manner that the probe is almost in contact with the medium (its gap is about the size of the minute opening, i.e., about 100 nm) having an uneven surface. Where a high-speed scanning is required, it is desirable to array the SNOM heads and perform a simultaneous scanning with multiple probes. In such a structure, the medium surface or the probe tip is likely to be damaged unless the SNOM heads are supported by different elastic bodies to scan the medium surface while each probe tip precisely follows and traces the surface.
In the case of the SNOM head, as illustrated in FIGS. 1, 2 and 3, the heads will probably be formed on a common substrate when the array is constructed. In such a structure, respective minute openings are present on a common plane, so that highly precise scanning of the medium surface is not possible. Therefore, another optical system for optical detection is needed, so the apparatus becomes large in size. Particularly where the arraying of the heads is to be designed, a preferable S/N of a detected signal is difficult to obtain due to the light interference and a relatively long distance between an observation point and a detecting system.
However, in the case where a plurality of the end-facet emitting lasers, as illustrated in FIG. 4, are arrayed, a plurality of supporting elastic bodies are needed. Therefore, the entire apparatus of the SNOM heads becomes large in size and heavy in weight, and hence a high-speed scanning is difficult to achieve.